MEMS technology has advanced to provide integrated packaging of different MEMS devices or sensors on a single chip. Although such integration offers significant advantages such as reduced requirements for commodity of space or “real estate”, it is often desirable to have different devices and sensors sealed at different pressures or different gas compositions when integrating multiple MEMS devices on the same chip. It will be recognized by those skilled in the art that such a need may arise where, for instance, different devices are sought to be optimized for different pressures or where different devices may require different ambient gasses or pressures (hereby referred to as ambient or ambients) to operate. For example, two hermetically sealed enclosures one containing a gyroscope and another containing an accelerometer would require different pressures, since a gyroscope requires a much lower pressure (vacuum) and accelerometer requires a pressure higher than that required for gyroscope for optimal performance.
It is often desirable to have different devices sealed at different pressures involving minimal processing steps, achieving a more predictable outcome through improved control, and having reduced requirements for the commodity of space or “real estate”. Therefore, it is desired to have a system and method that provides for two or more cavities with different pressures or different ambient gasses for operation on the same chip.
One approach to establish multiple pressures during the wafer bonding involves a method where a material is included in one of the enclosures that can absorb (getter) or desorb (outgas) gas molecules which can affect the pressure. In the case where the material has absorptive properties (getter) the pressure would decrease and in the case of desorptive properties (outgas) the pressure will increase. To achieve lower pressure, one of the enclosures may contain a gettering element that at elevated temperature absorbs at least one of the gasses present in the enclosure to decrease enclosure pressure. Similarly, to achieve higher pressure, one of the enclosures controls an outgassing source that, at elevated temperature, desorbs a controlled amount of one or more gases thereby increasing the enclosure pressure.
However, depending on the material of the getter and the outgasser and the gas absorbed, as in the case of gettering, or released, as in the case of outgassing, the gettering or outgassing material may require higher temperature for activation and/or acceleration of the absorption or desorption process. Therefore, there is a need to provide heating to the gettering or the outgassing material enclosed in the hermetically sealed chambers. Further what is needed is a system and method providing for the integration of such heaters into integrated CMOS-MEMS to create multi-ambient devices.